The present invention relates to switched capacitor (SC) amplifiers and, more particularly, to ratio-independent SC amplifiers capable of operating at high speeds.
A ratio-independent amplifier is used to double amplify (i.e., amplify with a gain of 2) a difference between two input signals, regardless of a mismatched capacitance ratio. For example, two capacitors in a conventional SC amplifier may be designed to have a ratio of one to one. However, it can be difficult to realize a precise capacitance ratio of one to one due to errors in device tolerances. As a result, a conventional SC amplifier may not output an amplified signal having a precise gain. Accordingly, a ratio-independent SC amplifier scheme provides a circuit that may be capable of outputting an amplified signal with a double gain despite device tolerances.
A ratio-independent switched capacitor amplifier may be used in a circuit requiring an amplifier with a double gain. For example, in general, a cyclic analog-digital converter and/or a pipeline analog-digital converter may include an amplifier circuit. The cyclic analog-digital converter and/or pipeline analog-digital converter may use a ratio-independent switched capacitor amplifier in order to double amplify a difference between input signals.
A conventional ratio-independent switched capacitor amplifier may include an operational amplifier, a capacitor, and a feedback capacitor. Although not shown in figures, the capacitor is connected to an inverting terminal of the operation amplifier, and the feedback capacitor is connected to an output terminal of the amplifier to form a feedback loop.
A ratio-independent switched capacitor amplifier samples/charges an input voltage on a sampling capacitor at a first stage and discharges the charged voltage (or charges) of the sampling capacitor to a feedback capacitor at a second stage. That is, during the second stage, charges stored in the sampling capacitor are sent to the feedback capacitor. Afterwards, an input voltage is again charged in the sampling capacitor at a third stage, and charges stored in the sampling capacitor are discharged to the feedback capacitor at a fourth stage. In accordance with the above-described approach, a ratio-independent switched capacitor amplifier may store double charges of an input voltage in a capacitor, and as a result may have a double gain of charges in the capacitor.
A ratio-independent switched capacitor amplifier may require four stages of operation, including two sampling stages, in order to obtain a double gain. Accordingly, the conventional manner approach may have a disadvantage, in that it is may not be suitable for applications needing high-speed amplifier operation.